Discharge-pumped excimer laser device

ABSTRACT

The present invention provides a discharge-pumped excimer laser device which includes a laser chamber filled with a laser gas that is deteriorated to a small extent, magnetic bearings and a motor that are resistant to the entry of dust particles, and parts that are held in contact with the laser gas and suffer little damage, and has a long service life. 
     The discharge-pumped excimer laser device according to the present invention has a laser chamber ( 1 ) filled with a laserigas and housing at least a pair of main discharge electrodes ( 2, 2 ) for producing an electric discharge to be able to oscillate a laser beam, housings ( 6, 7 ) joined to opposite sides of the laser chamber ( 1 ), a cross flow fan ( 3 ) having opposite ends rotatably supported by magnetic bearings ( 8, 9, 10, 11 ) accommodated in the housings ( 6, 7 ), for producing a high-speed laser gas flow between the main discharge electrodes ( 2, 2 ), a motor ( 12 ) accommodated in the housing ( 7 ) for rotating the cross flow fan ( 3 ), laser gas flow passages ( 61, 62 ) extending through gaps between rotor side and stator side of the magnetic bearings ( 8, 9, 10, 11 ) and the motor ( 12 ) over an axial entire length of the housings ( 6, 7 ), and communicating with an interior of the laser chamber ( 1 ), a laser gas introduction passage ( 60 ) extending from the interior of the laser chamber ( 1 ) and communicating with the laser gas flow passages ( 61, 62 ), and filters ( 20, 20 ) disposed in the laser gas introduction passage ( 60 ).

TECHNICAL FIELD

The present invention relates to a discharge-pumped excimer laserdevice, and more particularly to a discharge-pumped excimer laser devicehaving a cross flow fan rotatably supported by magnetic bearings, forgenerating a high-speed gas flow between a pair of main dischargeelectrodes.

BACKGROUND ART

FIG. 9 is a cross-sectional view showing a general structure of aconventional discharge-pumped excimer laser device of the type describedabove. As shown in FIG. 9, the conventional discharge-pumped excimerlaser device has preionizing electrodes (not shown) for preionizing alaser gas and a pair of main discharge electrodes 102, 102 for producingan electric discharge to be able to oscillate a laser beam, thepreionizing electrodes and the main discharge electrodes 102, 102 beingdisposed in a laser chamber 101 filled with a laser gas. The laserchamber 101 also houses therein a cross flow fan 103 for generating ahigh-speed gas flow between the main discharge electrodes 102, 102.

The cross flow fan 103 has a rotatable shaft 104 extending from oppositeends thereof and rotatably supported by bearings 106, 106 that aremounted in opposite sides of the laser chamber 101. The laser chamber101 has windows 105, 1051 for emitting the laser beam from the laserchamber 101 therethrough and a dust filter (not shown) for removing dustfrom the laser gas in the laser chamber 101.

The bearings 106, 106 by which the cross flow fan 103 is rotatablysupported are lubricated by a lubricant that usually comprises afluorine-based grease. It is known that the fluorine-based grease isleast degraded by a corrosive gas such as a fluorine-based gas used inthe discharge-pumped excimer laser device. However, the fluorine-basedgrease is problematic that it tends to be diffused in the laser gas andcauses a photochemical reaction with light generated by the electricdischarge and fluorine contained in the laser gas, producing impuritiessuch as CF₄, etc. which are liable to degrade the laser gas.

There has been proposed a discharge-pumped excimer laser device in whichcomponents of the bearings are coated with a solid lubricating film todispense with any grease. However, it has been pointed out that thesolid lubricant causes more friction in the bearings than the greaselubricant. In addition, since the solid lubricating film has a thicknessof up to 1 μm, it is likely to be peeled off when submicroscopic metaldust particles produced by the electric discharge in the laser chamberfind their way into the bearings.

There has also been proposed a process of positively introducing a lasergas from which dust particles have been removed into regions between thecross flow fan and the bearings with a view to protecting the bearings.It has also been proposed to make bearing holders of PTFE(polytetrafluoroethylene) that has an excellent lubricating capability.Since, however, the fluorine-based material is used, scraped dustparticles tend to be diffused into the laser chamber.

Because the discharge-pumped excimer laser device uses a halogen gaswhich is highly reactive with the laser gas, the laser chamber housestherein components which are made of Ni and Ni-plated metal materialsthat are highly resistant to halogen-induced corrosion. However, uponlaser oscillation, since the laser gas is excited by the electricdischarge between the discharge electrodes, the Ni and Ni-plated metalmaterials in the laser chamber are sputtered, thus producing an Nipowder and an Ni powder that has chemically reacted with the halogen gasin the laser gas.

Inasmuch as the Ni powder is ferromagnetic, if the contactless magneticbearings are used as the bearings and a motor is incorporated, then theNi powder is attached to and deposited on the magnetic material surfacesof the magnetic bearings and the motor, tending to obstruct the rotationof the cross flow fan. It has heretofore been customary to increase theclearance between the rotor and the stator as much as possible toprevent the rotation of the cross flow fan from being obstructed evenwhen dust particles are attached to the magnetic material surfaces ofthe magnetic bearings and the motor.

However, as the allowance for dust particles to be attached to themagnetic bearings and the motor increases, the clearance between therotor and the stator needs to be increased, resulting in a reduction inthe force for controlling the magnetic bearings. Generally, because theforce for controlling the magnetic bearings are reduced in proportion tothe square of the clearance, if the clearance is doubled and the forcefor controlling the magnetic bearings is to be maintained, then it isnecessary to use magnetic bearings in which the surface area of theelectromagnet is increased four times, or the number of turns of theelectromagnet is increased four times, or the coil control current isincreased twice.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above drawbacks. Itis a first object of the present invention to provide a discharge-pumpedexcimer laser device which includes a laser chamber filled with a lasergas that is deteriorated to a small extent, magnetic bearings and amotor that are resistant to the entry of dust particles, and parts thatare held in contact with the laser gas and suffer little damage, and hasa long service life.

A second object of the present invention is to provide adischarge-pumped excimer laser device which prevents dust particles fromentering magnetic bearings and a motor and can be continuously operatedover a long period of time.

To achieve the above objects, there is provided in accordance with aninvention described in claim 1, a discharge-pumped excimer laser device,comprising: a laser chamber filled with a laser gas and housing at leasta pair of main discharge electrodes for producing an electric dischargeto oscillate a laser beam; a cross flow fan having opposite endsrotatably supported by magnetic bearings, for producing a high-speedlaser gas flow between the main discharge electrodes; a motor forrotating the cross flow fan; laser gas flow passages extending throughgaps between rotor side and stator side of the magnetic bearings and themotor and communicating with an interior of the laser chamber; a lasergas introduction passage extending from the interior of the laserchamber and communicating with the laser gas flow passages; and filtersdisposed in the laser gas introduction passage.

With the above invention, the laser gas in the laser chamber flows fromthe laser gas introduction passage through the laser gas flow passagesback into the laser chamber. When the laser gas flows through the lasergas flow passages, the laser gas flows through the gap between thestator side and rotor side of the magnetic bearings by which the crossflow fan is rotatably supported and the gap between the stator side androtor side of the motor which rotates the cross flow fan, thus replacingthe gas in these gaps. Therefore, the working time required to removeimpurities from the discharge-pumped excimer laser device when it startsto operate is shortened, and the discharge-pumped excimer laser deviceis kept dust-free.

According to an invention described in claim 2, the discharge-pumpedexcimer laser device according to claim 1, wherein the magnetic bearingsand the motor are accommodated in housings joined to opposite sides ofthe laser chamber.

With the above invention, the laser chamber and the housings areseparate from each other, and can be serviced for maintenance andassembled with ease.

According to an invention described in claim 3, the discharge-pumpedexcimer laser device according to claim 2, wherein the laser gas flowpassages extend over an entire length of the housings and communicatewith the laser gas introduction passage at respective ends of thehousings.

With the above invention, the laser gas is caused to flow in onedirection in the laser gas flow passages over their entire length, andis prevented from being trapped in the laser gas flow passages.

According to an invention described in claim 4, the discharge-pumpedexcimer laser device according to claim 1, 2, or 3, wherein portions ofthe magnetic bearings and the motor which face the laser gas flowpassages are made of a material which is resistant to corrosion by thelaser gas or covered with a can made of a material which is resistant tocorrosion by the laser gas.

With the above invention, since the portions of the magnetic bearingsand the motor which face the laser gas flow passages are made of amaterial which is resistant to corrosion by the laser gas or coveredwith a can made of a material which is resistant to corrosion by thelaser gas, the corrosion resistance of the magnetic bearings and themotor is increased.

According to an invention described in claim 5, the discharge-pumpedexcimer laser device according to claim 4, wherein the material which isresistant to corrosion by the laser gas is permalloy, austeniticstainless steel, nickel-copper alloy, nickel-chromium alloy, ornickel-chromium-molybdenum alloy.

With the above invention, the stator side and rotor side of the motorand the stator side of the magnetic bearings are covered with a can ofaustenitic stainless steel or the like, and the rotor side of themagnetic bearings are made of a pure PC permalloy, so that the magneticbearings and the motor can have their service life extended can havetheir performance and efficiency increased, and can be reduced in size.

According to an invention described in claim 6, the discharge-pumpedexcimer laser device according to claim 1, 2, 3, 4, or 5, wherein adifferential pressure generating mechanism is disposed in the laser gasintroduction passage.

With the above invention, since the differential pressure generatingmechanism is disposed in the laser gas introduction passage, the lasergas is caused to flow reliably from the laser gas introduction passagethrough the laser gas flow passages back into the laser chamber. As aresult, dust particles are prevented from flowing into the magneticbearings and the motor.

According to an invention described in claim 7, the discharge-pumpedexcimer laser device according to claim 1, 2, 3, 4, or 5, wherein adifferential pressure generating mechanism is disposed in the laser gasflow passages.

With the above invention, since the differential pressure generatingmechanism is disposed in the laser gas flow passages, the laser gas iscaused to flow reliably from the laser gas introduction passage throughthe laser gas flow passages back into the laser chamber, and dustparticles are prevented from flowing into the housings joined to theopposite sides of the laser chamber. As a result, dust particles areprevented from flowing into the magnetic bearings and the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an overall structure of adischarge-pumped excimer laser device according to a first embodiment ofthe present invention;

FIG. 2 is a cross-sectional view showing details of a bearing housing ofthe discharge-pumped excimer laser device illustrated in FIG. 1;

FIG. 3 is a cross-sectional view showing details of a motor housing ofthe discharge-pumped excimer laser device illustrated in FIG. 1;

FIGS. 4A and 4B are views showing the shapes of side plates of a crossflow fan of the discharge-pumped excimer laser device illustrated inFIG. 1;

FIG. 5 is a diagram showing the results of a corrosion resistance testconducted on the fluorine of permalloys;

FIG. 6 is a cross-sectional view showing an overall structure of adischarge-pumped excimer laser device according to a second embodimentof the present invention;

FIG. 7 is a cross-sectional view showing an overall structure of adischarge-pumped excimer laser device according to a third embodiment ofthe present invention;

FIG. 8 is a cross-sectional view showing an overall structure of adischarge-pumped excimer laser device according to a fourth embodimentof the present invention; and

FIG. 9 is a cross-sectional view showing a structure of a conventionaldischarge-pumped excimer laser device.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to FIGS. 1 through 8.

FIGS. 1 through 4 show a discharge-pumped excimer laser device accordingto a first embodiment of the present invention. FIG. 1 is a crosssectional view showing an overall structure thereof, FIG. 2 is across-sectional view showing details of a bearing housing thereof, FIG.3 is a cross-sectional view showing details of a motor housing thereof,and FIGS. 4A and 4B are views showing the shapes of side plates of across flow fan thereof.

As shown in FIG. 1, a laser chamber 1 houses therein preionizingelectrodes (not shown) for preionizing a laser gas and a pair of maindischarge electrodes 2, 2 for producing an electric discharge to be ableto oscillate a laser beam. The laser chamber 1 also houses therein across flow fan 3 for generating a high-speed gas flow between the maindischarge electrodes 102, 102. The main discharge electrodes may beprovided in a plurality of pairs.

The laser beam is oscillated by a laser-pumping electric dischargeproduced when a high voltage is applied between the main dischargeelectrodes 2, 2. The generated laser beam is emitted out of the laserchamber 1 through windows 5, 5 disposed on side walls of the laserchamber 1. When the laser-pumping electric discharge is caused, thelaser gas present between the main discharge electrodes 2, 2 isdeteriorated and has its discharge characteristics lowered, failing toperform repetitive oscillation. To solve this problem, the cross flowfan 3 is rotated to circulate the laser gas in the laser chamber 1 toreplaced the laser gas between the main discharge electrodes 2, 2 ineach electric discharge cycle, to that the laser gas can stably beoscillated repetitively.

The distance between the main discharge electrodes 2, 2 is about 20 mm,and the entire length thereof is about 600 mm. The frequency of therepetitive oscillation of the laser gas is several thousand times asecond. The entire length of the cross flow fan 3 is slightly largerthan the length of the main discharge electrodes 2, 2 in order toachieve a uniform flow rate over the entire length of the main dischargeelectrodes 2, 2. The cross flow fan 3 is rotated at a speed ranging from2500 to 3500 min⁻¹ to obtain a sufficient gas flow that is requiredbetween the main discharge electrodes 2, 2. In the present embodiment,since a rotor is supported by magnetic bearings in a contactless manner,the upper limit for rotational speeds allowed by the bearing capabilityis several tens of thousands rpm. Therefore, the cross flow fan maycomprise a high-speed cross flow fan.

The cross flow fan 3 has a rotatable shaft 4 extending therethrough andextending from opposite ends thereof. The rotational shaft 4 isrotatably supported in a contactless manner by radial magnetic bearings8, 9, 10 and an axial magnetic bearing 11 that are accommodated in abearing housing 6 and a motor housing 7 which are disposed on oppositesides of the laser chamber 1. The motor housing 7 houses therein a motor12 for imparting rotational power to the rotatable shaft 4 of the crossflow fan 3.

The bearing housing 6 and the motor housing 7 also house thereinprotective bearings 13, 14, 15 which support the rotatable shaft 4 ofthe cross flow fan 3 when the radial magnetic bearings 8, 9, 10 are notin operation.

The bearing housing 6 and the motor housing 7 also house therein, nearthe laser chamber 1, screw groove labyrinth 16, 17 as differentialpressure generating mechanisms which rotate in unison with the rotatableshaft 4 for generating a differential pressure. In this embodiment, thescrew-type rotating labyrinth seal 16 has its screw grooves located onthe rotatable shaft 4 of the cross flow fan 3. However, the screwgrooves may be located in the bearing housing 6 and the motor housing 7.

The laser chamber 1 has a gas outlet port 18 which is connected to a gasintroduction port 6 e defined in an end of the bearing housing 6 and agas introduction port 7 c defined gin an end of the motor housing 7 by alaser gas introduction chamber 19 and gas inlet pipes 21, 21, thusmaking up a gas introduction passage 60. The laser gas introductionchamber 19 houses therein dust removing filters 20, 20.

The bearing housing 6 has a laser gas flow passage 61 defined thereinwhich extends through gaps between the rotors and stators of the radialmagnetic bearing 8 and the axial magnetic bearing 11, over the entireaxial length of the bearing housing 6, and communicates with theinterior of the laser chamber 1. The motor housing 7 has a laser gasflow passage 62 defined therein which extends through gaps between therotors and stators of the radial magnetic bearings 9, 10 and the motor12, over the entire axial length of the motor housing 7, andcommunicates with the interior of the laser chamber 1. The laser gasflow passages 61, 62 communicate with the laser gas introduction passage60 through the gas introduction ports 6 e, 7 c.

When the rotatable shaft 4 rotates to rotate the cross flow fan 3 andthe screw groove labyrinths 16, 17, the laser gas in the laser chamber 1flows from the laser gas introduction passage 60 through the laser gasflow passages 61, 62 back into the laser chamber 1. As the laser gasflows along the laser gas flow passages 61, 62, the laser gas flowsthrough the gaps between the rotors and stators of the magnetic bearings8, 9, 10, 11 by which the cross flow fan 3 is rotatably supported, andalso through the gap between the stator and rotor of the motor 12 whichrotates the cross flow fan 3.

As shown in detail in FIG. 2, the bearing housing 6 comprises a mainbearing housing body 6 a mounted on the side wall of the laser chamber1, a pair of electromagnet housings 6 b, 6 c, and a bearing cover 6 dhaving the gas introduction port 6 e defined therein. The radialmagnetic bearing 8 and the axial magnetic bearing 11 are accommodated inthe bearing housing 6. Sealing grooves 29, 31, 33, 35 are defined inmating surfaces of these components of the bearing housing 6, andsealing members 30, 32, 34, 36 are mounted respectively in the sealinggrooves 29, 31, 33, 35 to seal the laser gas. The sealing members 30,32, 34, 36 should preferably be made of metal such as stainless steel oraluminum, for example, which emits a small amount of gas such asmoisture that contaminates the laser gas.

The radial magnetic bearing 8 has a displacement sensor 8 a and anelectromagnet 8 b that are relatively positioned by a spacer 22 and aside plate 23, and housed in the main bearing housing body 6 a. A thincylindrical can 24 is inserted in the main bearing housing body 6 aagainst its inner circumferential surface, and has its opposite endsfixed as by welding to the main bearing housing body 6 a. With thisconstruction, the displacement sensor 8 a and the electromagnet 8 bwhich are constructed of silicon steel sheets and copper wire coils thatare not highly resistant to corrosion by the laser gas are held out ofcontact with the laser gas. The inner circumferential surfaces of thedisplacement sensor 8 a and the electromagnet 8 b may be provided withan isolation phase or partition wall of plated Ni or PTFE(polytetrafluoroethylene).

The axial magnetic bearing 11 has electromagnets 11 b, 11 c fixed inposition by the electromagnet housings 6 b, 6 c in facing relation toeach other. Thin disk-shaped cans 27, 27 are fixed as by welding tosurfaces of the electromagnets 11 b, 11 c. The axial displacement sensor11 a is housed in the bearing cover 6 d, and a thin disk-shaped can 28is fixed as by welding to a surface of the axial displacement sensor 11a which is held in contact with the laser gas, thus placing the axialdisplacement sensor 11 a out of the sealed chamber.

The cans 24, 27, 28 are made of austenitic stainless steel,nickel-copper alloy, nickel-chromium alloy, or Hastelloy(nickel-chromium-molybdenum alloy) which is highly resistant tocorrosion by the laser gas. Thus, the cans 24, 27, 28 are prevented frombeing corroded by the laser gas Since the cans 24, 27, 28 communicatedwith the laser gas chamber 1 are making up a sealing space, they need tohave a thickness large enough to withstand the sealed pressure (1-3kg/cm²) of the laser gas. Since the above materials are of highmechanical strength, the thickness of the cans can be reduced. Inaddition, since the above materials are nonmagnetic materials which donot obstruct lines of magnetic forces produced by the magnetic bearings,the magnetic bearings can efficiently be operated.

A displacement sensor target 8 c and an electromagnet target 8 d of theradial magnetic bearing 8 are relatively positioned by rotor spacers 25,26 and fixed to the rotatable shaft 4 of the cross flow fan 3. Adisplacement sensor target lid and an electromagnet target lie of theaxial magnetic bearing 11 are fixed to an end of the rotatable shaft 4,and placed in the sealed space that communicates with the laser chamber1.

The displacement sensor target 8 c and the electromagnet target 8 d ofthe radial magnetic bearing 8, and the displacement sensor target lidand the electromagnet target 11 e of the axial magnetic bearing 11 aremade of a magnetic material which comprises a pure PC permalloy (Fe—Nialloy containing 75-80% of Ni) that is highly resistant to corrosion byfluorine contained in the laser gas.

The PC permalloy may be replaced with PD permalloy (Fe—Ni alloycontaining 35-40% of Ni) or PB permalloy (Fe—Ni alloy containing 45-50%of Ni) that has a large saturated flux density and is suitable for useas an electromagnet material, with the PD permalloy or PB permalloybeing plated with Ni on its surface. The PD permalloy or PB permalloythus plated with Ni is as resistant to corrosion by the laser gas as PCpermalloy or more resistant to corrosion by the laser gas than PCpermalloy. The permalloy needs to be plated with a uniform and highlyadhesive layer of Ni in order to prevent a gas trap for contaminatingthe laser gas from being formed.

FIG. 5 is a diagram showing the results of a corrosion resistance testconducted on the fluorine gas of permalloys. As shown in FIG. 5, PCpermalloy (JISC2531) containing 80% of Ni is more corrosion-resistantthan austenitic stainless steel SUS316L. The resistance to corrosion bya fluorine gas of PB permalloy (JISC2531) containing 45% of Ni is aboutone-half of austenitic stainless steel SUS304, and hence PB permalloy(JISC2531) is less corrosion-resistant than PC permalloy. However, itcan be seen that PB permalloy that is surface-treated by Ni plating, forexample, is as corrosion-resistant as PC permalloy or morecorrosion-resistant than PC permalloy.

The protective bearing 13 comprises a rolling bearing having balls 13 amade of alumina ceramics, and inner race 13 b and outer race 13 c whichare made of stainless steel such as SUS440C. Since the protectivebearing 13 is disposed in the sealed space communicating with the laserchamber 111, the balls 13, the inner race 13 b and the outer race 13 care made of a material that is resistant to corrosion by the laser gas.Therefore, the protective bearing 13 in the present embodiment is notdeteriorated by the laser gas. Since the balls 13 a are made of aluminaceramics, the allowable rotational speed and allowable load of theprotective bearing 13 are increased, making itself suitable for use asthe protective bearing 13. While the protective bearing 13 is made ofthe above materials in the present embodiment, the balls 13 a may bemade of zirconia ceramics. The inner race 13 b and the outer race 13 cmay be made of alumina ceramics or zirconia ceramics.

The inner and outer races have rolling surfaces coated with a solidlubricant of polytetrafluoroethylene (PTFE). Since PTFE that is stableagainst the laser gas and has a high lubricating capability is used as asolid lubricant in the protective bearing 13, it does not deterioratethe laser gas. The solid lubricant is capable of making the service lifeof the bearing much longer than if no lubricant were used. Therefore,the protective bearing 13 does not need to be replaced over a longperiod of time. Alternatively, a solid lubricant made of lead or analloy of lead may be used as a lubricant.

The protective bearing 13 may comprise a ring made of PTFE. Since PTFEis a highly pure fluorine resin, it is highly resistant to weatheringand may be of a structure of few gas traps.

As shown in detail in FIG. 3, the motor housing 7 comprises a main motorhousing body 7 a mounted on the side wall of the laser chamber 1 and abearing cover 7 b having the gas introduction port 7 c defined therein.The radial magnetic bearings 9, 10 and the motor 12 are accommodated inthe motor housing 7. Sealing grooves 52, 54 are defined in matingsurfaces of these components of the motor housing 7, and sealing members53, 55 are mounted respectively in the sealing grooves 52, 54 to sealthe laser gas. The sealing members 53, 55 should preferably be made ofmetal such as stainless steel or aluminum, for example, which emits asmall amount of gas such as moisture that contaminates the laser gas.

A displacement sensor 9 a and an electromagnet 9 bof the radial magneticbearing 9, a stator 12 a of the motor 12, and a displacement sensor 10 aand an electromagnet 10 b of the radial magnetic bearing 10 arerelatively positioned by spacers 41, 42, 43 and a side plate 44, andaccommodated in the main motor housing body 7 a. A thin cylindrical can45 is inserted in the main motor housing body 7 a against its innercircumferential surface, and has its opposite ends fixed as by weldingto the main motor housing body 7 a. The can 45 is made of austeniticstainless steel, Hastelloy (nickel-chromium-molybdenum alloy), or thelike for the reasons described above. With this construction, thedisplacement sensor 9 a and the electromagnet 9 b of the radial bearing9, the displacement sensor 10 a and the electromagnet 10 b of the radialmagnetic bearing 10, and the stator 12 a of the motor 12 are preventedfrom contacting the laser gas.

A displacement sensor target 9 c and an electromagnet target 9 d of theradial magnetic bearing 9, a rotor 12 b of the motor 12, and adisplacement sensor target 10 c and an electromagnet target 10 d of theradial magnetic bearing 10 are relatively positioned by rotor spacers46, 47, 48, 49 and fixed to the rotatable shaft 4 of the cross flow fan4, and are placed in the sealed space that communicates with the laserchamber 1. As with the displacement sensor target 8 c and theelectromagnet target 8 d of the radial magnetic bearing 8, thedisplacement sensor targets 9 c, 10 c and the electromagnet targets 9 d,10 d are made of PC permalloy (Fe—Ni alloy containing 70-80% of Ni).However, the displacement sensor targets 9 c, 10 c and the electromagnettargets 9 d, 10 d may be made of PD permalloy (Fe—Ni alloy containing35-40% of Ni) or PB permalloy (Fe—Ni alloy containing 40-50% of Ni)plated with Ni on its surface.

A can 50 is attached to the outer circumferential surface of the rotor12 b of the motor 12 and fixed as by welding to side plates 51, 51, andthe side plates 51, 51 and the rotatable shaft 4 of the cross flow fan 3are fixed as by welding to each other, thus defining a sealed space tokeep the rotor 12 b out of contact with the laser gas. The can 50 ismade of austenitic stainless steel, Hastelloy(nickel-chromium-molybdenum alloy), or the like for the reasonsdescribed above.

As with the protective bearing 13 in the bearing housing 6, theprotective bearings 14, 15 comprise rolling bearings having balls 14 a,15 b made of alumina ceramics, and inner races 14 b, 15 b and outerraces 14 c, 15 c made of stainless steel such as SUS440C. Alternatively,the protective bearings 14, 15 may comprise rings made of PTFE.

FIGS. 4A and 4B show the shapes of side plates 3-1 attached to each ofthe opposite side ends of the cross flow fan 3. FIG. 4A shows anapertured side plate 3-1 having a plurality of holes 3-1 a, and FIG. 4Bshows a flat side plate 3-1 free of holes. If the side plate 3-1comprises a flat side plate free of holes 3-1 a, then it produces apumping effect to cause the laser gas to flow radially outwardly alongthe side plate 3-1 as indicated by the arrow A in FIG. 2.

If the side plate 3-1 comprises an apertured side plate, then the lasergas is caused to flow radially outwardly of the cross flow fan 3 throughthe holes 3-1 a as indicated by the arrow B in FIG. 2 due to the faneffect of the cross flow fan 3. As a result, a laser gas flow directedtoward the center as indicated by the arrow C in FIG. 2 is passivelyproduced. In addition, the laser gas is caused to flow toward the crossflow fan 3 as indicated by the arrow D in FIG. 2. The laser gas is alsocaused to flow similarly in the motor housing 7.

With the discharge-pumped excimer laser device thus constructed, whenthe cross flow fan 3 and the screw groove labyrinths 16, 17 are rotated,the laser gas flows from the laser gas introduction passage 60 throughthe laser gas flow passages 61, 62 back into the laser chamber 1. Thelaser gas is cleaned by the dust removing filters 20 in the laser gasintroduction chamber 19.

When the cleaned laser gas flows through the laser gas flow passage 61in the bearing housing 6, it flows through the gap between the rotorside (the displacement sensor target 11 d and the electromagnet target11 e) and the stator side (the axial displacement sensor 11 a and theelectromagnets 11 b, 11 c) of the axial magnetic bearing 11, and the gapbetween the rotor side (the displacement sensor target 8 c and theelectromagnet target 8 d) and the stator side (the displacement sensor 8a and the electromagnet 8 b) of the radial magnetic bearing 8, replacingthe gas in these gaps with the positively cleaned laser gas.

Since the rotor side (the displacement sensor target 11 d and theelectromagnet target 11 e) of the axial magnetic bearing 11 and therotor side (the displacement sensor target 8 c and the electromagnettarget 8 d) of the radial magnetic bearing 8 are made of PC permalloythat is highly resistant to corrosion by the laser gas, and the statorside (the axial displacement sensor 11 a and the electromagnets 11 b, 11c) of the axial magnetic bearing 11 and the stator side (thedisplacement sensor 8 a and the electromagnet 8 b) of the radialmagnetic bearing 8 are covered with the cans 28, 27, 24 made ofaustenitic stainless: steel, Hastelloy or the like, the corrosionresistance of the magnetic bearings 8, 11 is increased.

When the cleaned laser gas flows through the laser gas flow passage 62in the motor housing 7, it flows through the gap between the rotor side(the displacement sensor target 10 c and the electromagnet target 10 d)and the stator side (the displacement sensor 10 a and the electromagnet10 b) of the radial magnetic bearing 10, the gap between the rotor 12 band the stator 12 a of the motor 12, and the gap between the rotor side(the displacement sensor target 9 c and the electromagnet target 9 d)and the stator side (the displacement sensor 9 a and the electromagnet 9b) of the radial magnetic bearing 9, replacing the gas in these gapswith the positively cleaned laser gas.

Since the rotor side (the displacement sensor target 10 c and theelectromagnet target 10 d) of the radial magnetic bearing 10 and therotor side (the displacement sensor target 9 c and the electromagnettarget 9 d) of the radial magnetic bearing 9 are made of PC permalloythat is highly resistant to corrosion by the laser gas, the stator side(the displacement sensor 10 a and the electromagnet 10 b) of the radialmagnetic bearing 10, the stator side (the displacement sensor 9 a andthe electromagnet 9 b) of the radial magnetic bearing 9, and the stator12 a of the motor 12 are covered with the can 45 made of austeniticstainless steel, Hastelloy or the like, and the rotor 12 b of the motor12 is covered with the cap 50 made of austenitic stainless steel,Hastelloy or the like, the corrosion resistance of the magnetic bearings9, 10 and the motor 12 is increased.

FIG. 6 is a cross-sectional view showing a discharge-pumped excimerlaser device according to a second embodiment of the present invention.In FIG. 6, identical or corresponding parts are designated by the samereference numerals as those shown in FIGS. 1 through 4. Identical orcorresponding parts in other figures are also denoted by identicalreference characters. In the discharge-pumped excimer laser device shownin FIG. 6, cross flow fan units 70, 70 are disposed downstream of (inthe opposite ends of the gas introduction chamber 19) the dust removingfilters 20, 20 in the gas introduction chamber 19.

The cross flow fan units 70, 70 give the laser gas a differentialpressure to compensate for a pressure loss caused by the dust removingfilters 20, the gas introduction pipe 21, or the magnetic bearings 8, 9,10, 11 and the motor 12 in the bearing housing 6 and the motor housing7, allowing the laser gas to flow reliably. With the cross flow fanunits 70, 70, the laser gas flow from the laser chamber 1 through thelaser gas introduction passage 60 and the laser gas flow passages 61, 62back into the laser chamber 1 is promoted, and the laser gas flow fromthe laser chamber 1 through the laser gas flow passages 61, 62 issuppressed, thus preventing dust particles from flowing into themagnetic bearings 8, 9, 10, 11 and the motor 12.

FIG. 7 is a cross-sectional view showing a discharge-pumped excimerlaser device according to a third embodiment of the present invention.In the discharge-pumped excimer laser device shown in FIG. 7, axial flowfans 71, 71 are disposed in respective flow paths between the laserchamber 1 and the magnetic bearings 8, 9 disposed one on each side ofthe cross flow fan 3. The axial flow fans 71, 71 are fixed to therotatable shaft 4 of the cross flow fan 3 and rotatable in unison withthe cross flow fan 3 to produce a differential pressure. Since the gaspresent between the rotor side and stator side of the magnetic bearings8, 9, 10, 11 and the motor 12 has flowed through the dust removingfilters 20 and the gas introduction pipe 21, dust particles areprevented from flowing into the magnetic bearings 8, 9, 10, 11 and themotor 12.

FIG. 8 is a cross-sectional view showing a discharge-pumped excimerlaser device according to a fourth embodiment of the present invention.The discharge-pumped excimer laser device shown in FIG. 8 differs fromthe discharge-pumped excimer laser device shown in FIGS. 1 through 4 inthat it is free of the radial magnetic bearing 10 on the axial end ofthe motor 12. The radial magnetic bearing 10 on the axial end of themotor 12 serves to reduce vibrations of the motor 12 and allows themotor 12 to rotate stably if the motor 12 is large in size and tends toproduce large vibrations. Therefore, if the motor 12 is small in sizeand tends to produce small vibrations, then the radial magnetic bearing10 on the axial end of the motor 12 may be dispensed with as shown inFIG. 8.

According to the present invention, as described above, the laser gas inthe laser chamber flows from the laser gas introduction passage throughthe laser gas flow passages back into the laser chamber. When the lasergas flows through the laser gas flow passages, the laser gas flowsthrough the gap between the stator side and rotor side of the magneticbearings by which the cross flow fan is rotatably supported and the gapbetween the stator side and rotor side of the motor which rotates thecross flow fan, thus replacing the gas in these gaps. Therefore, theworking time required to remove impurities from the discharge-pumpedexcimer laser device when it starts to operate is shortened, and thedischarge-pumped excimer laser device is kept dust-free. Therefore, thedischarge-pumped excimer laser device is clean and has a long servicelife.

The portions of the magnetic bearings and the motor which face the lasergas flow passages may be made of a material that is highly resistant tocorrosion by the laser gas or covered with cans made of a material thatis highly resistant to corrosion by the laser gas, thereby making themagnetic bearings and the motor more resistant to corrosion. Thus, thedischarge-pumped excimer laser device has a long service life.

The differential pressure generating mechanism may be disposed in thelaser gas introduction passage or the laser gas flow passages, allowingthe laser gas to flow reliably from the laser gas introduction passagethrough the laser gas flow passages back into the laser chamber. As aconsequence, dust particles are prevented from flowing into and attachedto the magnetic bearings and the motor. The fan can thus be continuouslyoperated stably for a long period of time without its rotation beingobstructed.

INDUSTRIAL APPLICABILITY

The present invention can be applied as a discharge-pumped excimer laserdevice having a cross flow fan rotatably supported by magnetic bearings,for generating a high-speed gas flow between a pair of main dischargeelectrodes.

What is claimed is:
 1. A discharge-pumped excimer laser device,comprising: a laser chamber filled with a laser gas and housing at leasta pair of main discharge electrodes for producing an electric dischargeto be able to oscillate a laser beam; a cross flow fan having oppositeends rotatably supported by magnetic bearings, for producing ahigh-speed laser gas flow between said main discharge electrodes; amotor for rotating said cross flow fan; laser gas flow passagesextending through gaps between rotor sides and stator sides of saidmagnetic bearings and communicating with an interior of said laserchamber; a laser gas introduction passage extending from the interior ofsaid laser chamber and communicating with said laser gas flow passages;and at least one filter disposed in said laser gas introduction passage.2. A discharge-pumped excimer laser device according to claim 1, whereinsaid laser gas flow passages extend longitudinally over a total lengthof said magnetic bearings.
 3. A discharge-pumped excimer laser deviceaccording to claim 1, wherein said magnetic bearings and said motor areaccommodated in housings joined to opposite sides of said laser chamber.4. A discharge-pumped excimer laser device according to claim 2, whereinsaid laser gas flow passages extend over an entire length of saidhousings and communicate with said laser gas introduction passage atrespective ends of said housings.
 5. A discharge-pumped excimer laserdevice according to claim 1, 3, or 4, wherein portions of said magneticbearings and said motor which face said laser gas flow passages are madeof a material which is resistant to corrosion by the laser gas orcovered with a can made of a material which is resistant to corrosion bythe laser gas.
 6. A discharge-pumped excimer laser device according toclaim 5, wherein said material which is resistant to corrosion by thelaser gas is permalloy, austenitic stainless steel, nickel-copper alloy,nickel-chromium alloy, or nickel-chromium-molybdenum alloy.
 7. Adischarge-pumped excimer laser device according to claim 1, 3 or 4,wherein a differential pressure generating mechanism is disposed in saidlaser gas introduction passage.
 8. A discharge-pumped excimer laserdevice according to claim 1, 3 or 4, wherein a differential pressuregenerating mechanism is disposed in said laser gas flow passages.
 9. Adischarge-pumped excimer laser device according to claim 8, wherein thedifferential pressure generating mechanism comprises a screw groovelabyrinth.
 10. A discharge-pumped excimer laser device according toclaim 9, wherein the screw groove labyrinth is between the magneticbearings and the interior of said laser chamber.